How Can A Microwave Cook?

It was during a radar-related research project around 1946 that Dr. Percy Spencer noticed something unusual. He was testing a new vacuum tube called a magnetron when he discovered that the candy bar in his pocket had melted. Intrigued, he placed some popcorn kernels near the tube and watched with an inventive sparkle in his eye as the popcorn sputtered, cracked and popped all over his lab. The next morning, he tried putting an egg near the magnetron tube and as he moved in for a closer look just as the egg exploded and splattered hot yolk all over his amazed face. This leads to the invention of the microwave oven with the magnetron tube as its heart.


But what are microwaves? Microwaves are electromagnetic waves just like light, electricity (AC) and radio that travel in waves. Now, that wavelike motion as they travel is defined by the unit Hertz. Hertz is a unit of frequency that measures the number of cycles completed in a specified time as they travel. In our house, the electricity travels in 60 cycles of wavelike motion every one second. That means our house electricity has a frequency of 60 Hz. Microwaves has a frequency between 300 Million Hz (0.3 GHz) to 300,000 Million Hz (300GHz). Microwave ovens are designed to produce only 2.45GHz and some has 2.5 GHz.

Although microwave is just an electromagnetic wave just like light, electromagnetic waves at its frequency range display some interesting properties; water, fats and sugars absorb them. When they are absorbed they are converted directly into atomic motion. The molecules in water, fats and sugars react to the microwave energy, making their molecules vibrate and produce heat. Microwaves in this frequency range have another interesting property; they are not absorbed by most plastics, glass or ceramics. Metal reflects microwaves, which is why metal pans do not work well in a microwave oven.